1. Field of the Invention
The present invention relates to a method of producing a ceramic multi-layer substrate containing a resistor and/or a dielectric.
2. Description of the Related Art
In production of ceramic multi-layer substrates containing resistors and capacitors by a green sheet lamination method, problems occur. The ceramic materials for the substrates and those for the resistors and the dielectrics, the compositions are different, and the firing shrinking characteristics are also different. Thus, when the materials for the substrate, the resistor and/or the dielectric are laminated and simultaneously fired, the substrate tends to be deflected, cracked or distorted, which are caused by the different firing shrinking characteristics.
To solve the above-described problems, the following technique has been developed, as described, e.g., in Japanese Unexamined Patent Application Publication No. 9-92983 (Patent Document 1) p.2 to p.3. That is, to a ceramic green sheet having a resistor and capacitor (dielectrics and electrodes) printed and fired at a low temperature, another ceramic green sheet is laminated. Thus, a green substrate containing the resistor and the capacitor is formed. Then, dummy green sheets (alumina green sheets) which can not be sintered at the sintering temperature of the substrate are laminated to both of the sides of the green substrate. The green sheets and the green substrate are simultaneously fired at about 900° C. while they are pressed from the upper side thereof. Thereafter, the non-sintered dummy green sheets adhering to both of the sides of the fired substrate are removed, and thus, a capicator and resistor containing (CR) ceramic multilayer substrate is produced.
However, it is impossible according to this production method to adjust the resistance or capacitance for the resistor or capacitor contained in the multi-layer substrate by trimming after the green substrate is fired. Thus, the multi-layer substrate has problems in that the resistance or capacitance has a large dispersion.
As described, e.g., in Japanese Unexamined Patent Application Publication No. 1-295483, (Patent Document 2) p.2 to p.3, it has been suggested that a resistor be trimmed to adjust the resistance before a green sheet having the resistor printed thereon is laminated, and thereafter, the green sheet is laminated and fired.
Even if the resistor is trimmed for adjustment of the resistance before the lamination of the green sheet (i.e., before the firing), as described in Patent Document 2, it is difficult to control the amount of an glass component which permeates from the green sheet into the resistor during the subsequent firing, so that the resistance of the resistor is varied as a consequence of the different amounts of the glass component permeated into the resistor at firing. Moreover, when the ceramic and the resistor or the dielectric having different firing shrinking characteristics are laminated and simultaneously fired, bubbles are readily formed inside the resistor or the dielectric. The formation of bubbles also causes the dispersion of the resistance or the capacitance to be increased.
It has been proposed that a cavity (hole) is formed in a ceramic multi-layer substrate, so that a contained resistor is exposed at the bottom of the cavity, and can be trimmed for adjustment of the resistance after the substrate is fired.
However, ceramic multi-layer substrates of which the wiring densities are high and the sizes are small have been used in recent years. From the standpoints of the small spaces, the ceramic multilayer substrates can scarcely afford to have cavities which are formed for trimming of the contained resistors, respectively. Thus, it may not be feasible to form such cavities in many cases. Even if a fine cavity is formed in a small-sized ceramic multilayer substrate, a contained resistor can be accurately trimmed through the fine cavity only with much difficulty.